A standard buttonhole machine has a vertically reciprocal needle, a horizontally displaceable material support plate, a rotary stitch plate below the needle, means for feeding a lower thread up through the stitch plate, clamps for holding material on the material plate at the stitch plate, and means for rotating the stitch plate in one rotational sense, simultaneously displacing the material plate, and reciprocating the needle to form a buttonhole in the fabric and for rotating it in an opposite return rotational sense after formation of the buttonhole. Such a machine also feeds an upper thread down through the needle to the stitching location and also normally lays a thick cording thread into the buttonhole to reinforce it. The upper and lower threads pass through respective brakes that tension them.
Once such a buttonhole is formed the threads must all be cut. No loose ends should remain, so ideally tails a few centimeters long are left. These tails are tucked through the hole afterward and a solid bar tack closes the buttonhole and secures these tails in place to make a high-quality buttonhole.
Rather than do this clipping manually, a pneumatically powered apparatus is known which is attached to the material plate. It has a blade which cuts transversely across the cording and lower threads once the buttonhole is formed, normally with automatic actuation. Such a device is bulky, getting in the way when the machine is operated, and is relatively slow. In addition shops not disposing of compressed air normally are not willing to make the equipment investment to use such devices. Furthermore the cutters often leave thread tails that are too short, or they apply so much lateral pressure to these threads that they pucker the newly formed buttonhole.